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Thursday, November 6, 2008

Pushing the Boundaries of Life: Antarctica

A colony of Adelies on Humble Island, one of eight islets off Anvers Island where thousands of Adelies have nested for some 600 years. Over the last 25 years these Adelie colonies have declined sharply. Chinstrap penguins are moving rapidly into Adelie territory. Archaeological digs in penguin colonies indicate there probably were no chinstraps in this area until about 50 years ago, when average temperatures began to rise.

Ornithologist Bill Fraser stands on the smooth pebbly surface of a former large colony of Adelie penguins on Torgersen Island. Unlike the colony in the photo above, this nesting site has been used by fewer and fewer penguins over recent years. Analyzing climate data, island topography, and breeding statistics, Fraser believes climate change caused the loss of half of its 16,000 nesting Adelies. Warming temperatures and more open water make for greater snowfall and more difficult hunting for krill, affecting nesting success. These changes are seen in other Adelie colonies on the Antarctic peninsula, but elsewhere in Antarctica, climate change either is favorable to the birds or is not affecting them.

A male Adelie penguin, back from a long feeding trip, disgorges krill for its chick. Krill develop best under seasonal ice, so thinner, less extensive winter ice can reduce the size of the shrimp-like Antarctic staple. The tiny radio transmitter on this bird's back allows Dr. Fraser to monitor how far and for how long penguins hunt for food. For some colonies, hunting times are becoming longer and longer as diminished seasonal sea ice extends the distance from rookery to feeding ground.

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